The nitrogenase system is related to a broad class of enzyme systems in which MgATP hydrolysis is linked to conformational changes that are transduced within a multi-component complex. Included in this group are ras p2l, elongation factor Tu, and recA-protein. One manner in which to gain information about the various conformations induced by component protein complex formation and MgATP hydrolysis in nitrogenase is to create stable forms of the complex and determine their structures crystallographically. Several biochemical strategies, including site- directed mutagenesis, will be utilized to capture physiologically relevant forms of the nitrogenase Fe protein/MoFe protein complex. Determination and comparison of the various complex structures and available models should provide insight into how the components interact to facilitate MgATP dependent unidirectional electron transfer from the Fe protein to the MoFe protein. A better understanding of how these aspects of nitrogenase catalysis are intimately linked is clearly relevant to related processes that also utilize conformational changes induced by nucleotide binding and hydrolysis to drive processes such as cellular regulation, protein synthesis and DNA recombination.